when the turtle head of ones faeces pretudes to the extent that it touches the cloth which comprises ones underwear. A crude expression with a mighty impact.

-"I am ever so glad i wore baggy boxer shorts today".
-"really egbert why is that".
-well humbert to be quite frank i am touching cloth.
-oh you are desperate to empty your bowels and are finding it hard to keep the turtles head under reigns.
-quite, and now i am afraid the turtles head has broken through my anal gates and is causing one great discomfort.
-i see, well it is lucky you are wearing spacious boxer shorts for if you were wearing y fronts the turtle may have been crushed resulting in a mess in ones pants.
-never mind i am starting to quite enjoy the sensation it is similar to when you insert your penis through my cheeks to the brown.
-oh well i dont know why you are complaining in that case it would be more like a terrapin head as my penis is terribly small due to the inbred nature of my family.
-dont beat yourself up you make up for it with your 11 fingers.

A saying that is used when someone has waited FAR too long to have a shit. It
verbalises the possible condition that the lead end of a shit has protruded beyond the opening of the anus and has made contact with their undergarment.